Tomorrow is the feast of Palm Sunday, when Christians commemorate the triumphal entry of Jesus into Jerusalem. The crowds that greeted Christ are said to have carpeted his path with palm fronds, symbols of joy and victory in Jewish tradition.
According to Roy Vickery's excellent Dictionary of Plant Lore, Christians in many parts of Europe traditionally used willow as a substitute for palm when decorating their churches on Palm Sunday. The species most often used was Salix caprea, commonly known as pussy willow, goat willow or great sallow. Apparently the tradition has all but died out in England, now that "real" palm fronds can be obtained fairly easily. I'm not sure whether the use of willow still continues on the continent.
Here's a quote from 1530, attributed to Palsgr. Bulleyn, which I found in the OED:
"Palme, the yellow that groweth on wyllowes"
Pussy willow is still known as "palm" in some parts of Britain and Europe. One of my Flickr contacts tells me that Germans call it palmkätzchen, which literally translates as "palm cat". Perhaps Simon can tell us what it's called in Hungary...
The link between willow and palm is not without biblical precedent. In the Old Testament, the book of Leviticus states "And you shall take on the first day the fruit of splendid trees, branches of palm trees and boughs of leafy trees and willows of the brook, and you shall rejoice before the Lord your God seven days."
Elsewhere in the British Isles, yew was used in place of palm, giving rise to the feast's alternative name "Yew Sunday". Roy Vickery says that the practice was widespread in Ireland, where many Irish speakers know Palm Sunday as Domhnach an Iuir.
In Flora Britannica, Richard Mabey states that yew was also widely used in England, particularly in years when the date of Palm Sunday was too late to permit flowering willow branches to be gathered. A shortage of willow catkins was more likely to have been a problem in southern counties, where the flowering season begins and ends a few weeks earlier than in the north.
According to the OED, yew was traditionally known as "palm" in parts of Kent. In illustration, the dictionary cites a pub in Woodnesborough called 'The Palm Tree' which, in 1887, was said to "bear for its sign a clipped yew tree."
Incidentally, there's a pub near my home in Sheffield called The Palm Tree Tavern, but I've no idea how it got its name!
This is my contribution to Festival of the Trees 10.